From 1aedfb2cbcae090cb2ce81edad4ffb985ed674e2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Marek=20Lema=C5=84czyk?= <marek@lemanczyk.eu>
Date: Thu, 17 Jul 2025 00:21:15 +0200
Subject: [PATCH] Optimize long-list AddRange for stack

---
 .../RecyclableStack.AddRange.cs               | 43 +++++++++++++++++--
 .../RecyclableStackTests.cs                   | 38 ++++++++++++++++
 2 files changed, 77 insertions(+), 4 deletions(-)

diff --git a/Recyclable.Collections/RecyclableStack.AddRange.cs b/Recyclable.Collections/RecyclableStack.AddRange.cs
index c6afdab..62057dc 100644
--- a/Recyclable.Collections/RecyclableStack.AddRange.cs
+++ b/Recyclable.Collections/RecyclableStack.AddRange.cs
@@ -281,27 +281,62 @@ namespace Recyclable.Collections
                 return;
             }
 
+            EnsureCapacity(stack, stack._count + longCount);
+
             int blockSize = items._blockSize;
             int fullBlocks = (int)(longCount >> items._blockSizePow2BitShift);
             int lastBlockLength = (int)(longCount & items._blockSizeMinus1);
 
+            RecyclableArrayPoolChunk<T> chunk = stack._current;
+            int index = chunk.Index;
+            int chunkLength = chunk.Value.Length;
+
             for (int blockIndex = 0; blockIndex < fullBlocks; blockIndex++)
             {
                 T[] block = items._memoryBlocks[blockIndex];
-                for (int i = 0; i < blockSize; i++)
+                int sourceIndex = 0;
+                while (sourceIndex < blockSize)
                 {
-                    stack.Push(block[i]);
+                    if (index == chunkLength)
+                    {
+                        chunk.Index = index;
+                        Grow(stack);
+                        chunk = stack._current;
+                        index = chunk.Index;
+                        chunkLength = chunk.Value.Length;
+                    }
+
+                    int toCopy = Math.Min(chunkLength - index, blockSize - sourceIndex);
+                    Array.Copy(block, sourceIndex, chunk.Value, index, toCopy);
+                    sourceIndex += toCopy;
+                    index += toCopy;
                 }
             }
 
             if (lastBlockLength > 0)
             {
                 T[] block = items._memoryBlocks[fullBlocks];
-                for (int i = 0; i < lastBlockLength; i++)
+                int sourceIndex = 0;
+                while (sourceIndex < lastBlockLength)
                 {
-                    stack.Push(block[i]);
+                    if (index == chunkLength)
+                    {
+                        chunk.Index = index;
+                        Grow(stack);
+                        chunk = stack._current;
+                        index = chunk.Index;
+                        chunkLength = chunk.Value.Length;
+                    }
+
+                    int toCopy = Math.Min(chunkLength - index, lastBlockLength - sourceIndex);
+                    Array.Copy(block, sourceIndex, chunk.Value, index, toCopy);
+                    sourceIndex += toCopy;
+                    index += toCopy;
                 }
             }
+
+            chunk.Index = index;
+            stack._count += longCount;
         }
 
         [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.AggressiveOptimization)]
diff --git a/Recyclable.CollectionsTests/RecyclableStackTests.cs b/Recyclable.CollectionsTests/RecyclableStackTests.cs
index 4d91bfc..60d5ffd 100644
--- a/Recyclable.CollectionsTests/RecyclableStackTests.cs
+++ b/Recyclable.CollectionsTests/RecyclableStackTests.cs
@@ -404,5 +404,43 @@ namespace Recyclable.CollectionsTests
             _ = stack.Should().Equal(expected);
         }
 
+        [Theory]
+        [MemberData(nameof(RecyclableLongListTestData.ItemsCountTestCases), MemberType = typeof(RecyclableLongListTestData))]
+        public void AddRangeShouldAddLongListItemsInCorrectOrder(int itemsCount)
+        {
+            long[] data = RecyclableLongListTestData.CreateTestData(itemsCount).ToArray();
+            using var source = new RecyclableLongList<long>(data);
+            using var stack = new RecyclableStack<long>();
+
+            stack.AddRange(source);
+
+            List<long> expected = new(itemsCount);
+            expected.AddRange(data);
+            expected.Reverse();
+
+            _ = stack.Count.Should().Be(itemsCount);
+            _ = stack.Should().Equal(expected);
+        }
+
+        [Theory]
+        [MemberData(nameof(RecyclableLongListTestData.ItemsCountTestCases), MemberType = typeof(RecyclableLongListTestData))]
+        public void AddRangeShouldNotOverrideItemsFromLongList(int itemsCount)
+        {
+            long[] data = RecyclableLongListTestData.CreateTestData(itemsCount).ToArray();
+            using var source = new RecyclableLongList<long>(data);
+            using var stack = new RecyclableStack<long>();
+
+            stack.AddRange(source);
+            stack.AddRange(source);
+
+            List<long> expected = new(itemsCount * 2);
+            expected.AddRange(data);
+            expected.AddRange(data);
+            expected.Reverse();
+
+            _ = stack.Count.Should().Be(itemsCount * 2);
+            _ = stack.Should().Equal(expected);
+        }
+
         }
 }